The present invention relates to magnetic workholding devices, and, in particular, to a compact modular switchable permanent-electro magnetic device that may be deployed with respect to other such devices without magnetic influence therebetween.
Magnetic holding systems employing electromagnets have been extensively used in applications requiring substantial magnetic force. In contrast with permanent magnets which have only one active state, the electromagnets may be selectively magnetized and demagnetized in achieving the desired activity. Inasmuch as the magnetized state is negated by intentional or inadvertent power loss, the possibility exists that magnetic field may be interrupted during lifting, transferring or holding activities thereby causing damage to surrounding property and personnel.
In an effort to overcome problems associated with power loss, switchable permanent-electromagnetic systems have been proposed. Therein, momentary activation reverses the polarity of a reversible magnet thus providing two stable magnetic states for the system; an active state wherein the magnetic field is coupled with the associated workpiece and an inactive state wherein the magnetic field is internalized. While performing satisfactorily in discrete environments, in order to achieve sufficient magnetic forces in larger applications involving substantial and irregular areas, a multiplicity of such magnets are generally required. Because of geometrical and deployment limitations, numerous problems can be presented. Generally, such systems must be arranged in prescribed biaxial arrays, generally based on square or rectangular poles. Accordingly, the flux paths are orthographically prescribed and dependent on surrounding poles. Such orientation results in excessive flux paths and heights in the workpiece as well as residual stray flux patterns in the workpiece that can undesirably reduce magnetic performance and attract particulate contaminants. Preferably the systems should operate at magnetic saturation in order to optimize performance and minimize sizing. Such operating conditions are difficult to attain in current geometrical arrays wherein the inherent variations in each magnetic subset also affect surrounding magnets. Accordingly time consuming assembly and testing is required, magnet by magnet, to avoid adverse cumulative effects in the assembled system. Furthermore, the need to maintain the prescribed pole patterns limits the ability to provide magnetic coupling at external or internal peripheries such as around workpiece openings and the like. Thus, notwithstanding advances over permanent magnet and electromagnet systems, the prior switchable permanent electromagnetic systems have not yielded uniform magnetic coupling, consistent manufacture, and flexibility of disposition.
For example, U.S. Pat. No. 2,348 to Laubach discloses a permanent lifting magnet whereby an electromagnet is energized to neutralize the effect of a main permanent magnet thereby releasing workpieces being transported.
U.S. Pat. No. 6,002,317 to Pignataro discloses an electrically switchable magnet system wherein a solenoid switched magnet is used to selectively provide an active and inactive magnetic condition for the system.
U.S. Pat. No. 4,956,625 to Cardone et al. discloses a magnetic gripping apparatus wherein paired pole units having permanent magnets interposed therebetween may be switched between an active and inactive magnetic condition.
U.S. Pat. No. 4,090,162 to Cardone et al. discloses a magnetic anchoring apparatus using longitudinally spaced pole sets separated by a permanet bridging magnet wherein one pole is alternatively conditioned by a switchable permanent magnet to provide an active and inactive magnetic condition.
U.S. Pat. No. 4,507,635a to Cardone et al. discloses a magnetic anchoring apparatus having quadrangular arrayed square poles separated by permanent bridging magnets.
U.S. Pat. No. 5,270,678 to Gambut et al. discloses a longitudinal series of paired square magnetic poles that are solenoid switched between magnetic states.
U.S. Pat. No. 5,041,806 to Enderle et al. discloses an electromagnetic holding device having concentric annular poles coupled with a radially polarized permanent magnet with the inner pole being magnetically reversed by a solenoid to effect magnetic states.
U.S. Pat. No. 4,777,463 to Cory et al. discloses a magnetic fixture assembly having a base with a permanent magnet which normally clamps a plate thereto but which is disabled to release the plate when an electromagnet is energized.
Therefore, a need exists for a switchable permanent electromagnet that can be readily manufactured and assembled to consistent and optimum specifications, disposed in flexible arrays without interference with or interdependence on surrounding magnets, and consistently operated at magnetic saturation.
The present invention accomplishes the foregoing needs by providing a switchable permanent electromagnet module that operates readily at magnetic saturation and low flux heights with flexible orientation of coupling with the workpiece, individually or in combination with other modules.
The module comprises an annular switchable inner pole surrounded by an outer pole field of similarly equal planar surface area to the inner pole. The inner pole is coupled to the outer pole with an annular permanent magnet and with a switchable permanent magnet controlled by an electromagnetic field. In an inactive state, the flux path is internalized through the module allowing unrestrained movement of the workpiece. In the active state, a flux path is established externally, radially and circumferentially between the coupling surfaces of the inner pole and the outer pole, through the workpiece with a shallow flux height. The outer pole may be variably geometrically configured with respect to the inner pole, requiring only sufficient area to permit the inner pole to achieve saturation. In individual modules, the outer pole is preferably a concentric annulus capable of achieving saturation. However, the outer pole may constitute a surrounding field in which other modules are deployed. Therein, the modules may be oriented for optimum coupling with the workpiece, substantially without regard to the location of adjacent modules. Even when positioned within overlapping outer pole annuli, the radial and circumferential flux distribution accommodates saturation without affecting surrounding magnets. Because of the lack of magnetic interference, the modules may be manufactured and tested, prior to unit assembly, solely for individual module performance and without regard to surrounding conditions. Further, inasmuch as the modules, either with integral outer poles or field outer poles, only require machined bores for assembly the overall rigidity of the magnet holding device is not adversely affected, in contrast with geometrical pole arrays wherein substantial areas must be removed for housing the magnet system. In addition to flexible relative position, the modules may also be deployed in varying relationships. Generally, the pole faces lie in a single plane transverse to the magnetic axis. However, varying inclined, multiple plane and irregular surfaces may be magnetically coupled at saturation.